Since track-bound, and in particular rail-guided, vehicles for high-speed, regional and local transport have been equipped virtually exclusively with bogie-type running gears, so-called individual-wheel running gears have also recently become established. Whereas bogies have two or more sets of wheels or four or more so-called individual wheels, and are thus very heavy, individual-wheel running gears have two individual wheels, and individual-wheel-set running gears have one set of wheels.
In the case of track curves, bogies are steered by the leading set of wheels or the leading individual wheels. The small axle spacing or wheel spacing means that the wheels travel through curves with only a small amount of noise and low wear, and two or more bogies beneath the carriage body provide for stable guidance along a rectilinear track at relatively high speeds. Additional steering of the sets of wheels or individual wheels in the bogie is achieved by the diagonal connection between two sets of wheels or by utilizing the angular movements of leading and trailing carriage bodies.
Two-wheeled individual-wheel running gears have become widespread, in particular, in local and regional transport. Individual wheels make it easier in design terms to provide for simple entrance into carriages by virtue of the carriage floor being lowered to a level of approximately 300 mm, which is the case in so-called low-floor vehicles. If the so-called rolling condition, which is characterized by virtually identical rolling and circumferential speeds for the wheels which are respectively on the inside and outside of the curve, and the so-called adjustment condition, which describes the adjustment of the wheel planes tangentially, or of the wheel axles radially, with respect to the rails, are maintained, there is a virtually physically ideal reduction in wear and noise, and thus a high degree of comfort. Various methods are used in order to realize this ideal track guidance.
"Nahverkehrs-Praxis", no. 11/1992, p. 402 ff., discloses a three-part articulated vehicle with, in each case, two individual-wheel running gears per carriage body. Two individual wheels are arranged in one wheel carrier and, for each carriage, two wheel carriers are mounted in the running gear frame of the carriage body so as to be pivotable about the vertical pin in each case. The vertical king pin for the pivot pin is located in the center between the wheels of the wheel carrier, in the plane of symmetry of the vehicle. The curve-dependent pivoting or steering of the wheel carriers is effected by an additional steering linkage with respect to the pin-free articulation. In this case, the steering linkage is moved in dependence on the articulation angle between the carriage bodies, and the articulation angle is adjusted in a curve-dependent manner, with the result that the wheel carriers can be adjusted approximately radially with respect to the curve. Similar positively controlled steering of individual-wheel running gears, with, in each case, two individual wheels per running gear and a portal-like articulated structure, was developed in Austria (cf. ZEV+DET Glas. Annalen 116 (1992) no. 8/9, p. 333 ff.).
An individual-wheel running gear with self-regulating individual wheels is described in DE 34 09 103 A1 and DE 37 44 983 C2. Each of the individual wheels can be steered about a dedicated vertical pivot pin. The individual-wheel carriers, which are located opposite one another on the inside and outside of the curve, are connected by a track rod. By way of the vertical pivot pins, which are located outside the stand-up points of the wheels, the forces produced during wheel/rail contact are utilized in order to guide the wheel planes back tangentially with respect to the rail, with the result that the wear between wheel and rail is reduced considerably.
EP 02 95 462 B1 discloses an individual-wheel running gear structure which is equipped with actuating devices. Two individual wheels are arranged in a wheel carrier, and two wheel carriers are mounted in a running gear frame so as to be pivotable about the vertical in each case. The king pin, which actually forms the vertical pivot pin, is located in the centre between the wheels of a wheel carrier, in the plane of symmetry of the running gear frame. The curve-dependent pivoting of the wheel carriers is effected by one actuating device for each wheel carrier. The actuating is supported on the running gear frame and, in dependence on an adjacent carriage body connected to the carriage body in an articulated manner, pivots each wheel carrier about the fixed pivot in the wheel-carrier center.
With curve control for individual wheels which is configured in dependence on the carriage-body articulation angle, the error in the adjustment which is correct for the curve increases as the articulation angle increases. Furthermore, it is not possible to achieve precise tangential positioning of the individual-wheel planes in the transition curve. The numerous articulations and connections of the steering linkage require a not inconsiderable amount of outlay for maintenance and adjustment.
In the case of individual-wheel running gears with self-regulating, individually driven individual wheels, the influence of traction forces on the steering behavior may result in undesired travelling movement. In terms of production and heat, differential drive torques between the traction motors cannot be avoided, and these torques result in differential traction forces which may lead to undesired steering. These differential traction forces may also result from tolerance-dependent or transverse-displacement-dependent changes in the radius of the rolling circle of the driven individual wheels. Furthermore, with very small track-curve radii and a large axle spacing, there is a reduction in the gauge of these individual wheels steered in such a manner.
If the wheel carriers, which can be rotated about a vertical pin, are made to pivot by hydraulic actuating members, then a need for a not inconsiderable amount of space and high energy outlay should be expected since the wheel/rail contact forces which counteract the steering movement have to be overcome by the actuating members. When the vehicle is travelling through a curve, failure of a hydraulic actuating member constitutes a risk to travelling safety. If the influence of the traction forces on the track guidance cannot be eliminated, then the hydraulic actuating members additionally have to compensate traction-force differences.